Variable inductance device



May 22, 1951 v. J. COOPER VARIABLE INDUCTANCE DEVICE 2 Sheets-Sheet 1 Filed Sept. 27, 1947 INVENTOR VICTO JAMES COOPER BY A ATTORNEY y 1951 v. J. COOPER 2,554,295

VARIABLE INDUCTANCE DEVICE Filed Sept. 27, 1947 2 Sheets-Sheet 2 INVENTOR VICTOR JAMES COOPER ATTORNEY Patented May 22, 1951 VARIABLE INDUCTANCE DEVICE Victor James Cooper, Writtle, England, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application September 27, 1947, Serial No. 776,517 In Great Britain September 30, 1946 15 Claims.

This invention relates to variable coupling arrangements, transformers and variable inductance devices generally for use on very high frequencies.

Great difficulties are experienced in producing satisfactory variable inductance devices for use on very high frequencies where a range of frequencies has to be covered, more particularly in the case of coupling arrangements for use in wide band amplifiers, mainly owing to the stringent requirements of keeping down self-capacity in the device and maintaining a high coupling coefiicient.

The present invention seeks to provide improved variable inductance devices suitable for use for the purposes mentioned which shall be simple in construction, easy to manufacture and satisfactory electrically.

According to this invention a variable inductance device comprises at least two substantially parallel longitudinal conductors arranged to con stitute an interrupted turn and means for varying the spacing between said conductors to vary the inductance presented at terminals constituted by the ends of the interrupted turn.

Preferably there are two pairs of parallel conductors mounted eccentrically on discs or cranks which are arranged to be rotated together in such manner that upon rotation the spacing between the individual conductors varies so that said conductors lie at the corners of an imaginary rectangle or square which can be expanded or contracted by rotating the discs or cranks.

Preferably a fixed coupling coil is provided at some convenient position in the space between the conductors.

Again preferably the conductors are in the form of straight metal tubes.

The invention is illustrated in the accompanying drawings in which Fig. 1 shows in simplified schematic manner one embodiment of the invention; Fig. 2 shows with more detail and in sectional elevation one of the eccentric conductors of the arrangement of Fig. 1; Fig. 3 illustrates a modification; and Fig. 4 illustrates a further modification of the invention.

Referring to Figs. 1 and 2, four straight tubular conductors I are mounted parallel to one another by means of circular end plate assemblies 2 to which they are eccentric, each conductor being between two plate assemblies. At one end El there are four circular conductin end assembles (only two appear in Fig. l) which are indirectly geared together by means of stub axles 8 and gear wheels 3 of insulating material (only two gears appear in Fig. I) or are otherwise rotatably arranged in such manner that in one extreme position of rotation the four conductors are in close proximity while in the other extreme position they are remote from one another. At this end of the system the four assemblies 2 are effectively connected together through a common conducting plate 4. Such connection may be effected through suitable spring contacts I attached to stationary circular end plates l2, in turn connected to the common conducting plate 4. The connection may be either directly or by means including a very low impedance capacity coupling which is provided, in the example illustrated, by inserting a sheet 5 of dielectric between the common c0nducting plate 4 and a pair of conducting plates 6 each of which is connected directly to two stationary end plates [2. At the other end E2 of the system the conductors are mounted upon circular plate assemblies 2 which are, however, arranged in pairs, each pair being insulated from the other pair. The said pairs of assemblies are similarly connected directly or indirect 1y to terminal plates 9, l0 which constitute the inductance device terminals.

A coupling coil H consisting of one rectangular turn is mounted in a mean position in the space between the conductors with its longer sides parallel to the conductors, the position of said coupling coil being such as'not to interfere with the rotation of the conductors. Coupling coil H as shown is formed from a length of coaxial transmission line 13 bent to form 2. rec-- tangle and having the inner conductor connected to the outer conductor of the end thereof. By means of coil H the circuit formed by an inductor according to the invention is coupled to a following circuit.

With the arrangement of Figs. 1 and 2 there are in effect two rectangular inductance loops in parallel, each of constant length and variable width, and upon rotation the proximity of these two loops is varied, the spacing being thus a function of the effective loop width. With this arrangement it will be seen that by suitable dimensioning of the parts high degrees of coupling may be obtained with a relatively high degree of constancy.

In a modification shown by Fig. 4, the two pairs of conductors are cross-connected to constitute two loops in series, each-loop being of constant length and variable width, the spacing being again a function of the loop width during rotation. In this modification the front conducting plate is arranged in two parts 4?) and do which plates are insulatingly spaced by any suitable means (not shown). The rear conducting plate is in four parts 90., 5b, Ida, lilo. The rear conducting plates are also insulatingly spaced by any suitable means (not shown). The insulating gears, circular conducting end assemblies, and the coupling coil 5 i are omitted in Fig. 4. only in the interest of simplifying the drawing as they all form the same mechanical structure as in Fig. 1. The difference between the structure of Fig. 1 and that of Fig. 4 being that the front and rear conducting plates are divided to permit the arrangement of an electrical circuit for which an additional connection lead C is required for cross-connecting the two diagonally opposed rear conducting plates 91) and its together. This modification forms an electrical circuit which connects all the four loops I in series. ternal terminal connections to the loops are made directly to the diagonally opposed plates 9a and tab by any suitable ineas (not shown).

In another modificat'on of the above described arrangement shown in Fig. 5, the four conductors are utilized in pairs, each pair eing efiectively connected together (i. e., either directly or through very low impedance) at the same or at opposite ends of the system by means of suitable spring contacts. In this modification front and rear conducting plates are arranged in three sec-- tions, 411, 3c, and M, and 9c, 9d, and 3e, respectively, which sections are insulatingly spaced. by any suitabl means (not shown). The insulating gears and circular conducting end assembl'es are omitted in Fig. 5 in the interest of Sllld" plifying the drawing, as they all form the same mechanical structure as shown in In this way two similar variable inductances of variable spacing and equal magnitude and coupled t0- gether are provided to constitute the primary and secondary of a radio frequency transformer whose resonant frequency may be varied-by vary ing the spacing of the conductors as already described. The external terminal connections to the loops are made directly to end plates 4e and 4i and 9c and to by any suitable means.

The invention is not limited to the provision of fixed coupling coil as above described nor to the use of four conductors. In some cases the coupling coil can be dispensed with. Further the invention may be carried into practice by using only two conductors arranged parallel to one another so that their spacing can be varied. Such an embodiment is illustrated in Fig. Here U- there are two parallel tubular conductors l on the ends of cranks 2a, so that they can rotate about eccentric axes, the conductors being connected together at ta through their cranks at one end El and being rotated together in any convenient manner (not shown). At the other end E2 the conductors are connected through the cranks 2a to the terminals 9, iii of the inductance. The two-conductor systems as above described may be employed in combination to provide an embodiment in which, by changing over the end connections, the loops constituted by each pair of conductors may be placed in series or in parallel, as may be desired.

What is claimed is:

1. A variable inductance device including two pairs of elongated conductors arranged substantially parallel to each other to define a parallelepiped, the conductors of each pair being connected together at one end to form interrupted turns,

.and means for. simultaneously rotating said 4 conductors about axes eccentric to the axes of said conductors to vary the spacing between said conductors to vary the inductance value presented at the unconnected ends of said pairs of conductors.

2. A variable inductance device including two elongated conductors arranged side by side and substantially parallel to each other, said conduc .tors being connected together at one end to form an interrupted turn, and means for rotating at least one of said conductors about an axis eccentrio to the axis of that conductor to vary the spacing between said conductors to vary the inductance value presented at the unconnected ends of said conductors.

3. A variable inductance device including two elongated conductors arranged side by side and substantially parallel to each other, said conductors being connected together at one end to form an interrupted turn, and at least one of said conductors being arranged ,on crank elements for rotatable movement about an axis eccentric to the axis of that conductor to vary the spacing between said conductors to vary the inductance value presented at the unconnected ends of saidconductors.

.4. A variable inductance device including two elongated conductors arranged side by side and substantially parallel to each other, said conductors being connected together at one end to form an interrupted turn, and means for rotating said conductors about axes eccentric .to the axes of the respective conductors to vary the spacing between said conductors to vary the inductance value presented at the unconnected ends or said conductors.

5. A variable inductance device including .two elongated conductors arranged side by side and substantially parallel .to each other, conducting end plate members, crank members arranged on said end plate members and affixed to the ends of said conductors, said conductors being connected together at one end .by the conductive end plate thereat to forman interrupted turn, and means for simultaneously rotating said conductors on said crank members to vary the spacing between said conductors to vary the inductance value presented at the unconnected ends of said conductors.

6. A variable inductance device including two elongatedconductors arranged side by sid and substantially parallel to each other, conducting end plate members crank members arranged on said end plate members and afiixed to the ends of said conductors, said conductors being connected together at one end by the conductive end plate thereat to form an interrupted turn, spring contact members associated with said crank members to insure electrical contact between ,said conductor and said end plate members,.and-means ior simultaneously rotating said conductors on saidcrank members to 'vary the spacingbetween said conductors to vary the-inductance value presented at the unconnected ends of said conductors.

'7. A device as claimed in claim 1, wherein there areprovided a plurality of discs, said :two pairs of parallel conductors, being mounted eccentrically on said discs, each of said ,discs being arranged to be rotated together in such manner that upon rotation the spacing between the individual conductors varies so that said conductors ,lie at the corners of an imaginary rectanne which can b e nd or co tra ted b r tatina he discs.

8. A device as claimed in claim. 2, wherein a fixed coupling coil is provided in the space between the conductors.

9. A device as claimed in claim 2, wherein the conductors are straight metal tubes.

10. A device as claimed in claim 1, wherein the conductors ar effectively connected together at one end and. effectively connected together in pairs at the other.

11. A device as claimed in claim 1, wherein the two pairs of conductors are cross-connected to constitute two loops in series, each loop being of constant length andwariable width.

12. A device as claimed in claim 1, wherein the four conductors are utilized in pairs, each pair being effectively connected together at the same end of the device to provide two similar variable inductances of variable spacing and equal magnitude and coupled together to constitute the primary and secondary of a radio frequency transformer, the resonant frequency of said transformer being varied by varying the spacing of the conductors.

13. A variable inductance device comprising two pairs of conductors, each pair of conductors being insulated from the other pair, a plate having bearing means for providing an axis of rotation for said conductors, and means for mounting each one of said conductors eccentric with respect to the axis of rotation thereof, and means for rotating the conductors so that they lie at the corners of an imaginary square which can be expanded or contracted.

14. A variable inductance device comprising two substantially parallel longitudinal conductors, said conductors being arranged for rotation and to constitute an interrupted turn, means for simultaneously varying the spacing between said pair of conductors, said means including a plurality of cranks, said conductors being individually mounted eccentrically on different cranks, said cranks being arranged to be rotated together in such a manner that upon rotation thereof the spacing between the individual conductors lying at the corners of an imaginary rectangle can be expanded or contracted.

15. A variable inductance device comprising two pairs of conductors, each pair of conductors being insulated fromthe other pair, a plate having bearing means for providing an axis of rotation for said conductors, and means for mounting each one of the conductors eccentrically with respect to the axis thereof, means for rotating the conductors so that they lie at the corners of an imaginary rectangle which can be expanded or contracted, and a dielectric member interposed between said plate and said mounting means for effectively connecting the conductors together through a low impedance capacitive coupling.

VICTOR JAMES COOPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,175,710 Usselman et a1. Oct. 10, 1939 2,405,174 Alford Aug. 6, 1946 2,407,282 Johnson Sept. 10, 1946 FOREIGN PATENTS Number Country Date 747,762 France June 23, 1933 

